Paracrine factors of stromal origin may regulate growth of the trophoblast during gestation. Recently we characterized mRNA expression of hepatocyte growth factor (HGF) and its receptor (c-met) in rhesus monkey placental samples obtained at 35, 36, 38, 40, 45, 60 70, 90, 120, 124, 144, 150, 154, and 157 days of pregnancy. The placental tissue was dissected free of endometrial decidua and a sample of placenta was fixed for histological characterization. Total RNA was prepared from placental samples and analyzed for HGF mRNA by Northern blot. Total RNA was also analyzed from human M426 cells (which secrete HGF) and MCF-7 (which do not express HGF). Northern blots revealed that HGF transcripts were present in placenta from all gestational ages. However, the signal for HGF increased dramatically during pregnancy with the strongest signal evident in the latest stages (144-154 day). c-met was also detected in placental RNA by Northern blot, but there was no evidence of increased or decreased regulation with gestational age. We conclude that the HGF paracrine system is present in the rhesus monkey placenta and may play a more important role during the late rather than the early gestational phases of placental growth.